1. Field of the Invention
This invention relates to a process for selectively producing para-ethyltoluene or para-diethylbenzene in an amount and of a quality which can be subsequently directly oxidized to terephthalic acid without the necessity of intermediate purification.
2. Description of the Prior Art
Terephthalic acid is an important chemical, representing an intermediate in the manufacture of synthetic fibers such as "Dacron". It has heretofore been commercially produced by oxidation of para-xylene employing various oxidation techniques. A significant cost, both for capital and operation, to obtain a product of greater than 99 percent para-xylene of fiber grade quality has necessitated expensive separation and purification steps to remove close boiling by-products. In addition, a costly step has generally been required to isomerize the ortho- and meta-isomers to the desired para and to remove ethylbenzene prior to subjecting the para-xylene product to oxidation.
Alkylation of aromatic hydrocarbon utilizing crystalline aluminosilicate catalysts has heretofore been described. U.S. Pat. No. 2,904,697 to Mattox refers to alkylation of aromatic hydrocarbons with an olefin in the presence of a crystalline metallic aluminosilicate having uniform openings of about 6 to 15 Angstrom units. U.S. Pat. No. 3,251,897 to Wise describes alkylation of aromatic hydrocarbons in the presence of X- or Y-type crystalline aluminosilicate zeolites, specifically such type zeolites wherein the cation is rare earth and/or hydrogen. U.S. Pat. No. 3,751,504 to Keown et al. and U.S. Pat. No. 3,751,506 to Burress describe vapor phase alkylation of aromatic hydrocarbons with olefins, e.g., benzene with ethylene, in the presence of a ZSM-5 type zeolite catalyst.
The disproportionation of aromatic hydrocarbons in the presence of zeolite catalysts has been described by Grandio et al. in the Oil and Gas Journal, Vol. 69, No. 48 (1971). U.S. Pat. Nos. 3,126,422; 3,413,374; 3,598,878; 3,598,879 and 3,607,961 show vapor-phase disproportionation of toluene over various catalysts.
While the above-noted prior art is considered of interest in connection with the subject matter of the present invention, the conversion process described herein, utilizing a crystalline aluminosilicate zeolite catalyst of specified characteristics which has undergone a particular preliminary treatment involving steaming, impregnation with phosphorus, followed by impregnation with magnesium and controlled pre-coking has not, insofar as is known, been heretofore described.